We propose to investigate the occurrence of four biologically active peptides (VIP, substance P, enkephalins, and bombesin) in the respiratory systems of human subjects and selected animal species. First, we will use fluorescent immunocytochemical methods to describe the localization and distribution of these four peptides in the larynx, trachea, main bronchi, and lungs. Then, using ultrastructural immunocytochemical methods, we will identify and characterize their subcellular localization. Finally, we will use simultaneous immunocytochemical and histochemical methods to investigate the possibility that some of these peptides may coexist in the same locations with known cholinergic or adrenergic neurotransmitters. This study should provide information about the locations and possible sites of action of these four biologically active peptides in the respiratory system.